The invention concerns a flake ice machine and a method for monitoring a flake ice machine.
Flake ice machines produce relatively thin flake ice for keeping food fresh, in particular in the meat industry. The cooled evaporator roller is immersed into the water of the evaporator trough. When the evaporator roller turns, the amount of water carried along by its jacket freezes. The ice layer thereby produced is released from the jacket of the evaporator roller by a means provided on the roller, e.g. a scraper, before renewed immersion into the water. This is effected either by scraping or cracking. The evaporator roller contains a refrigerant which is connected to a refrigerator located outside of the roller. A control means is provided for monitoring and controlling the evaporator roller, the refrigerator and the water inlet valve. To prevent damage to the flake ice machine or the evaporator trough due to overflow caused by malfunction, the control means monitors the filling time, ice production and water fill level in the evaporator trough. If predetermined thresholds are exceeded or fallen below, the water inlet valve, the drive of the evaporator roller or the refrigerator are switched off and the user receives an error message.
A sensor has been conventionally used to monitor the water fill level in the evaporator trough. If a maximum water fill level is detected, the control means triggers the closing of the water inlet valve. The water fill level in the evaporator trough decreases due to ice production. If the sensor detects a minimum water fill level in the evaporator trough, the water inlet valve is opened and the water fill level in the evaporator trough increases. This process is repeated as often as necessary. If the sensor is defective, the maximum water fill level is not detected and the water inlet valve is not closed, as a result of which the evaporator trough can overflow. If the user is not aware of this situation, serious water damage can result.
The temporal change of the water fill level has also been conventionally monitored. If the water fill level does not change within a predetermined time interval, the flake ice machine is defective. Possible defects are stoppage of the roller, freezing of the roller, a defect in the water fill level sensor, the water inlet valve or the water inlet. Monitoring of one value, namely the temporal change of the water fill level permits detection of all these defects, however, the cause of the error initially remains unknown and must be additionally determined.
In contrast thereto, the inventive flake ice machine and the inventive method have the advantage that the opening time of the water inlet valve is limited by a clock. The clock is started when the water inlet valve is opened. The water inlet valve is closed if either the sensor detects the maximum water fill level or when a predetermined filling time has elapsed. The filling time is set such that, when the flake ice machine operates faultlessly, filling up to the maximum water fill level is possible and the evaporator trough cannot overflow within the filling time. If the water inlet valve is switched off due to expiration of the filling time, the user receives an error message. In this case, either the sensor for determining the maximum water fill level or the water inlet valve is defective or water inlet does not occur for other reasons.
In an advantageous embodiment of the invention, the minimum water fill level can also be monitored in addition to monitoring the maximum water fill level. Towards this end, the clock is started when the water inlet valve closes. When the flake ice machine operates properly, the water fill level is reduced when the water inlet valve is closed due to ice production and discharge of the ice flakes. When the minimum water fill level has been reached, the water inlet valve opens again. A minimum sensor is provided for detecting the minimum water fill level. If the minimum water fill level is not detected either because the minimum sensor is defective or due to a halt in ice production, an error message is issued to the user after a predetermined discharge time has elapsed. The user can check the function of the flake ice machine and possibly switch it off.
Monitoring of the flake ice machine is possible not only during operation but also when restarting the flake ice machine after stoppage. In this case, the sensor initially detects whether the evaporator trough is filled to the maximum. If this is the case, the residual water valve opens until the sensor can no longer detect maximum fill level. The residual water valve is needed in order to remove the residual or dirty water in the trough after prolonged flake ice machine stoppage times so that same is not used for the production of ice. Opening of the residual water valve starts operation of a clock. After a predetermined time one checks whether or not the fill level is still at a maximum. If this is the case, the user receives an error message. This error message can be caused by a defective sensor or a defective residual water valve. Faultless function of the residual water valve is necessary in order to satisfy the high requirements for the flake ice machine concerning hygiene, since the flake ice is used in the food industry. As mentioned above, discharge of residual or dirty water must be guaranteed. Conventional flake ice machines do not detect a defect of the residual water valve since only the operating state is monitored. The operating state is not influenced by a defective residual water valve since that valve is not used during operation.
If after stoppage and renewed start of the flake ice machine the maximum fill level is not reached, the water inlet valve is opened and a clock is started. If a predetermined time is exceeded without detecting the maximum fill level, the user receives an error message. Possible causes can be a defective sensor, a defective water inlet valve, or a stoppage of water inlet due to other reasons. Usually, the monitoring intervals when starting the flake ice machine after stoppage are different than those during operation.
This method also checks whether water is present in the evaporator trough when starting the flake ice machine after stoppage. In known methods and devices, a sensor is used which determines the electrical conductivity of the evaporator trough content. Towards this end, e.g. two electrodes which are insulated from the evaporator trough may be provided at the bottom of the evaporator trough thereby utilizing the fact that water conducts electrical current and air acts like an insulator. The inventive method and the inventive device recognize the presence of water in the evaporator trough without checking the conductivity. This eliminates the problems which arise with water types having a low conductance, such as distilled water, and the disadvantages associated with electrolysis of water by the two electrodes.
The inventive method and the inventive device can also be combined with known methods and devices having temporal monitoring of the water fill level. In this case, a defective water inlet, water inlet valve or sensor for determining the maximum or minimum fill level can be detected by the inventive method. If the water fill level does not change with time, either the roller or refrigerator is defective. This permits determination of the source of error. If the above-mentioned method is also used to control the flake ice machine before operation start, complete monitoring of the flake ice machine is ensured.
Float switches are e.g. suitable as sensors for determining the maximum or minimum fill level in the evaporator trough. Advantageously, such switches do not depend on the chemical and physical properties of the liquid to be frozen. A float switch can also detect the maximum and the minimum water fill level. Only one float switch is therefore required in the evaporator trough.
When the minimum level is reached, the water inlet valve is opened with a delay of e.g. 15 seconds. This reduces the water level below the predetermined minimum before renewed water inlet. This assures that changes in the water surface, e.g. the formation of waves, do not repeatedly trigger the contact actuated by the sensor, which would otherwise cause rapid wear of that contact. A delayed closing of the water inlet valve when the maximum has been reached is also possible.
The control means comprises a logic circuit which effects opening or closing of the water inlet valve or of the residual water valve, depending on the situation, and optionally issues an error message to the user.
Further advantages and advantageous embodiments of the invention can be extracted from the following description, the drawing and the claims.